1. Field of the Invention
The present invention relates to a laser beam scanning apparatus for controlling the driving of a scanning unit including a laser unit by means of a control means provided on a print circuit board.
2. Related Background Art
An example of an image forming system using the laser beam scanning will be explained. FIG. 1 shows a block diagram of a laser beam printer embodying an image forming system.
Explaining each of the blocks, a scanning unit 104 is constituted by a laser unit 120, a detecting element 131 for detecting a horizontal synchronous signal for determining a scanning start position of the laser, a lens 121 for focusing a light beam 132 from the laser unit 120 onto an image bearing member 117, a reflection mirror 122 for directing the light beam 132 to the image bearing member and the like.
The reference numeral 109 denotes a toner image forming unit and a transfer unit for forming a toner image in response to image information and for transferring the toner image onto a recording sheet S.
More particularly, around a photosensitive member 117 acting as the image bearing member, there are disposed a pre-exposure lamp 115, a primary charger 114, a developing device 113 including toner therein, a transfer charger 112 and a cleaner 116; and, in response to the light beam 132 from the scanning unit 104, the toner image is formed on the image bearing member 117 and the toner image is transferred onto the recording material such as a sheet.
A fixing unit 106 serves to thermally fix the toner image on the recording sheet S by passing the latter between a heat roller 119 and a pressure roller 130.
A conveying unit 105 serves to separate the recording sheet S one by one from a sheet stack contained in a cassette 129 by means of a supply roller 110 and convey the recording sheet separated in a timed relation with the image timing to a pair of regist rollers 111 and then convey the recording sheet on which the toner image is transferred through the transfer charger 112 to the fixing unit 106.
Next, the relation between the blocks will be explained.
When signals for forming the image are sent to an image control unit 100 and a sequence control unit 103 through an interface 123 from a host computer 102 which is an external equipment acting as an image information source, these control units perform the following controls:
(i) driving the conveying unit 105 to separate and feed the recording sheet one by one; PA1 (ii) treating the image signal inputted from the external equipment 102 and the horizontal synchronous signal from the horizontal synchronous signal detecting element 131 in the scanning unit 104, whereby the synchronized image signal is sent to the laser unit 120 and a latent image is formed on the image bearing member 117 in the toner image forming unit by illuminating the light beam 132 onto the image bearing member (now charged) in response to the image signal; and controlling a current to be flowed into the light emitting element on occasion to keep the light amount of the light beam 132 constant; PA1 (iii) driving the developing device 113 to visualize the latent image formed on the image bearing member with the toner; PA1 (iv) driving the toner image forming unit, transfer unit 109 and conveying unit 105 to transfer the toner image on the image bearing member onto the recording sheet S; incidentally, the residual toner remaining on the image bearing member from which the toner image has been transferred is removed from the image bearing member by means of the cleaner 116; and PA1 (v) driving the fixing unit 106, thereby thermally fixing the toner image onto the recording sheet S conveyed from the transfer unit, thus finishing the image formation.
By the way, the above-mentioned various units (104, 109,105, 106) are disposed at predetermined locations in the scanning apparatus for functional and constructural reasons. Consequently, the control units 100, 103 were connnected to the various units via relatively long electrical signal distributing cables to permit the communication therebetween.
However, if the control units 100, 103 were arranged remote from the scanning unit 104 and these were interconnected through the signal distributing cables, the following disadvantage arose. That is to say, the signals emitted from and sent to the scanning unit directly relate to the image formation and are extremely high speed image signals. Thus, if the communication of such high speed image signals between the control units and the scanning unit was effected through the relatively long signal distributing cables, there arose a problem that the image signals were not properly transmitted due to the noise entering into the cables and the noise emitted externally from the cables, thus preventing the proper image formation.
To solve this problem, a method for shielding the signal distributing cables or a method for inserting a ferrite core in the cable has been adopted; however, these methods make the apparatus very expensive. Further, there is the limitation in preventing the noise, and, regarding the electric signal having a high frequency for obtaining the high resolving power, it was very difficult to prevent the noise.